Rebecca J. Stahl, MA
Western equine encephalitis (WEE) is a virus spread by a bite from an infected mosquito. While WEE is rare, an infected person can become seriously ill and even die from the virus.
WEE is caused by being bitten by a mosquito that is infected with the virus.
Factors that may increase your risk of WEE include:
Most people with WEE do not have any symptoms.
If symptoms do occur, they appear within 5-10 days after infection and include:
WEE can lead to more serious, life-threatening symptoms like inflammation of the brain (encephalitis), seizures, and
coma. These serious symptoms are more common in infants and older adults.
In addition to taking your medical history and doing a physical exam, your doctor will ask you:
Your doctor may need to test your bodily fluids. This can be done with:
Your doctor may need pictures of structures inside your head. This can be done with:
Because the infection is viral, there is no specific treatment for WEE. Treatment will focus on managing your symptoms and related complications through:
There is no vaccine for humans. There is a vaccine for horses. Prevention of WEE focuses on controlling mosquitoes and avoiding mosquito bites. Steps you can take to avoid mosquito bites include:
Centers for Disease Control and Prevention
National Institute of Allergy and Infectious Diseases
About Western equine encephalitis. Minnesota Department of Public Health website. Available at:
http://www.health.state.mn.us/divs/idepc/diseases/weencephalitis/basics.html. Accessed January 4, 2013.
Eastern equine encephalitis. EBSCO DynaMed website. Available at:
https://dynamed.ebscohost.com/about/about-us. Updated July 13, 2012. Accessed January 4, 2013.
Fact sheet: Western equine encephalitis. Centers for Disease Control and Prevention website. Available at:
http://www.cdc.gov/ncidod/dvbid/arbor/weefact.htm. Updated November 7, 2005. Accessed January 4, 2013.
Meningitis and encephalitis fact sheet. National Institutes of Neurological Disorders and Stroke website. Available at:
http://www.ninds.nih.gov/disorders/encephalitis_meningitis/detail_encephalitis_meningitis.htm. Updated February 16, 2011. Accessed January 4, 2013.
Reimann CA, Hayes EB, et al. Epidemiology of neuroinvasive arboviral disease in the United States, 1999-2007.
Am J Trop Med Hyg.
Western equine encephalitis fact sheet. Minnesota Department of Public Health website. Available at:
http://www.health.state.mn.us/divs/idepc/diseases/weencephalitis/wee.html. Accessed January 4, 2013.
10/1/2013 DynaMed Systematic Literature Surveillance
https://dynamed.ebscohost.com/about/about-us: Reimer LJ, Thomsen EK, Tisch DJ, et al. Insecticidal bed nets and filariasis transmission in Papua New Guinea. N Eng J Med. 2013 Aug 22; 369(8):745-753.
Last reviewed December 2013 by David L Horn, MD, FACP
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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